GAGeorgia Geography

Georgia's northern boundary is supposed to sit on the 35th parallel. The line James Camak marked on the ground in 1818 runs about a mile south of it, and that mile still matters, because the true parallel would place a bend of the Tennessee River inside Georgia. The legislature has demanded a resurvey more than once, most loudly in 2008 while Atlanta's reservoirs were dropping through a severe drought. Tennessee has declined every time, and the surveyed line stands.

Five provinces between Lookout Mountain and the sea

At 57,906 square miles of land, Georgia is the largest state east of the Mississippi River, and it crosses five physiographic provinces on the way from its northwest corner to the Atlantic.

• Appalachian Plateau. The far northwest tip only, flat topped sandstone country: Lookout Mountain and Sand Mountain.
• Valley and Ridge. Long parallel folds of limestone and shale around Rome and Dalton, the same structure that runs the length of the Appalachians.
• Blue Ridge. The high northeast, where Brasstown Bald reaches 4,784 feet and Springer Mountain, 3,782 feet, marks the southern terminus of the Appalachian Trail. Tallulah Gorge cuts about 1,000 feet deep across two miles.
• Piedmont. Rolling crystalline bedrock under deep red clay, holding most of the population. Stone Mountain, a granite pluton, stands 825 feet above it.
• Coastal Plain. Marine sands and clays covering more than half the state, split into an upper and lower section.

The fall line put three cities where they are

Where hard Piedmont rock meets soft Coastal Plain sediment, rivers drop. That boundary crosses Georgia diagonally through Columbus, Macon and Augusta, and all three exist for the same two reasons: boats coming up from the sea could go no further, and the falls turned mill wheels. Their positions on a map are not a coincidence but a straight reading of the geology.

The fall line is also an old shoreline. The sand hills around Augusta are relict beach deposits from a time when the ocean reached that far inland, and the sandy soils south of the line behave nothing like the clay to the north. Providence Canyon in Stewart County shows what happens when that sand is mistreated: gullies up to 150 feet deep, cut entirely since the 1800s by row crop farming, with no river involved at all.

Atlanta sits on a ridge, not a river

The Eastern Continental Divide crosses the Piedmont directly through Atlanta. Rain falling on one side of it drains to the Chattahoochee and eventually the Gulf of Mexico. Rain on the other side goes to the Ocmulgee, then the Altamaha, then the Atlantic.

Ridges make easy railroad grades, and that is the entire reason the city is there. The settlement began in 1837 as the end of the line for the Western and Atlantic Railroad and was called Terminus before it was called anything else. Atlanta is one of very few large American cities founded on neither a navigable river nor a coast, and its chronic water anxiety follows directly: the Chattahoochee is still a modest stream where it passes the metro area, which is what put Georgia, Alabama and Florida into a legal fight over that basin that has run since 1990.

Georgia's other defining rivers mark its edges. The Chattahoochee forms roughly 200 miles of the Alabama border before becoming the Apalachicola in Florida. The Savannah forms the entire South Carolina border, and under the 1787 Treaty of Beaufort the line lies at the far bank at low water, so every island in the river belongs to Georgia.

A swamp that drains two directions

The Okefenokee covers about 438,000 acres in the southeast corner, a peat bog sitting in a shallow basin that was a coastal lagoon when sea level stood far higher. Its eastern edge is dammed by Trail Ridge, a relict barrier island and dune system up to 150 feet high that has kept the water in place ever since.

Because the basin is nearly level, it spills two ways. Water leaves the western side into the Suwannee River, which crosses Florida to the Gulf of Mexico, and the eastern side into the St. Marys River, which reaches the Atlantic and doubles as part of the Florida state line. Peat beneath the swamp runs up to 15 feet thick, tannins stain the water the colour of strong tea, and the Hitchiti name usually rendered as land of the trembling earth describes the way the peat mat quakes underfoot.

A hundred miles of coast holding a third of the East's salt marsh

Measured in a straight line, Georgia's coast is only about 100 miles long, the shortest of any Atlantic state. Traced around every creek and island it comes to 2,344 miles of tidal shoreline.

The reason is the Georgia Bight, the inward curve of the southeastern coast between Cape Hatteras and Cape Canaveral. That concave shape funnels the incoming tide and amplifies it, so tidal range along Georgia runs 6 to 9 feet, roughly double what Florida beaches see and the largest on the South Atlantic coast. All that water moving twice a day built and sustains around 368,000 acres of salt marsh, close to a third of all the salt marsh on the United States East Coast.

Fourteen barrier islands sit offshore, including Cumberland, the largest at about 17.5 miles long, plus Sapelo, Ossabaw, St. Simons, Jekyll and Blackbeard. Only four can be reached by car, and most of the rest are held in conservation or research status. Inland, the state's temperature records run from 112 degrees Fahrenheit at Louisville on July 24, 1952 to minus 17 at a Civilian Conservation Corps camp near Rome on January 27, 1940.

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